Mechanism for generating the helical thread on grinding worms for gear grinding machines



y 22, 1958 I A. RICKENMANN 2,844,137

MECHANISM' FOR GENERATING THE HELICAL THREAD ON GRINDING WORMS FOR GEARGRINDING MACHINES Filed Sept. 17, 1956 5 Sheets-Sheet 1 ly 1958, A.RICKENMANN 2,

a MECHANISM FOR GENERATING-THE HELICAL THREAD on v GRINDING WORMS FORGEAR GRINDING MACHINES 1 Filed Sept. 17, 1956 3 Sheets-Sheet 2 fi 1? R9/JW wk I N 5 E NE July 22, 1958 I4QICKENMAN N 2,844,137 ING THE HELICALTHREAD ON GEAR GRINDING MACH s MECHANISM F0 Sheets-Sheet 3 A R GENERATGRINDING WORMS FOR Fig. 5

Filed Sept. 17, 1

MECHANISM FOR GENERATING THE HELICAL "THREAD ON GRINDING WORMS FOR GEARGRINDING MACHINES Alfred Rickenmann, Kusnacht, nearZurich, Switzerland,assignor to Reishauer-Werkzeuge A. G., Zurich, Switzerland ApplicationSeptember 17, 1956, Serial No. 610,132 Claims priority, applicationSwitzerland June 11, 1956 2 Claims. (Cl. 12511) The present inventionrelates to gear grinding machines operating according to the generatingprinciple, and has the general object of producing accurate grindingworms for such grinding machines.

The grinding worm used as the grinding tool in gear grinding machines ofthe kind referred to is mounted on the grinding spindle of the geargrinding machine and has a tooth rack profile in the sectionperpendicular to the helix angle. The dimensions thereof as regardsthepressure angle and pitch correspond normally to the basic rack profileof the toothing to be ground. In order to be able to grind gears on geargrinding machines of the kind referred to which gears are to have highaccuracy of profile it is an indispensable necessity that the portionsof the grinding worm which are active in the grinding process aredressed with outstanding accuracy for the working operation. a Thepresent invention has the'special object of producing a pitch of thehelical thread of the highest possible accuracy and freedom from wobble.Accordingly it is not directed to the'devices required for the finishingof the flanks. of the grinding worm as required for the dressing of forexample straight profile flanks, but exclusively to the mechanism whichguides such devices over the helical thread of the grinding tool. Eversince gear grinder machines operating according to the generatingprinciple have been" made, a lead screw withlead screw nut have beenused' for the production of the helical thread of the grinding worm. Thedrive of the lead screw is effected from the spindle on which thegrinding worm to be dressed is mounted, through various transmissionelements including a change gear train. The latter is selected inaccordance with the pitch to'be produced. The lead screw nut is in adirect con-' nection to a carriage which carries the dressing .deviceproper. This carriageis displaced during the dressing operation paralleltothe axis of the spindle at a speed which is accurately determined bythe rotational speed and by the pitch of the grinding worm to begenerated.

"Ihe accuracy attainable in these conditions of the pitch of thegrinding worm depends on the accuracy of the machine components formingpart of the transmission mechanism described hereinabove. If veryaccurate grinding worms are to be produced-as required for the grindingof first class gearsattention is called in the first place to the use ofaccurate lead screws, lead screw nuts and gears which must comply withhigh requirements in true-running and pitch.

-It is well known in the art that in spite 'of fulfilling all thesedetail requirements the accuracy desired is.in many cases not attained,which means that the present standing of.the art does not permit to keepbelow certain tolerances. It is to be remarked that the errors stillexisting ice on the grinding worm are caused by a sum of separateerrors. The following sources of errors are to be mentioned in the firstplace:

(1) Run-out errors of the change gears.

(2) Accumulative and adjacent pitch errors of the change gears.

(3) Pitch errors of the lead screw.

(4) Wobbling errors of the lead screw.

(5) Faults in the axial bearings of the lead screw.

The Wobbling errors of the lead screw is the deviation. of the actuallyexisting helix from the theoretical helix.

(the development of which is a straight line), Within one helical turn.It happens frequently that the lead screw checked in one plane ofmeasuring has an excellent pitch accuracy but is on the other handfraught with Wobbling errors, the magnitude of which exceeds the pitcherror ascertained in the aforesaid plane of' measuring.

Of necessity the sources of errors mentioned hereinabove make themselvesfelt somehow. It is quite possible that various faults may add up duringone working phase, and on the other hand may partly compensate oneanother. The result on the finished profiled grinding worm consists inthat errors of different magnitude are to be found. When then theproblem is set to reduce the errors still present this can be attainedwith the means hitherto known only in that elements of machinery areused which are practically free from any faults. quently gears and leadscrews of extraordinarily high accuracy have to be fitted. Theproduction thereof would involve such extraorbitant costs that theywould hardly be bearable economically.

grinding worms in question can be made at narrower tolerances thanhitherto without requiring the machinery elements of the dressingmechanism to have abnormally high accuracy. The idea of the inventionconsists in that the displacement imparted by the lead screw to the leadscrew nut per revolution of the grinding worm amounts to a multiple ofthe pitch of the grinding worm to be generated, and that thelongitudinal movement of the lead screw nut is transmitted by means of alever transmission to the carriage designed for accommodating thedressing device and is at the same time reduced at the ratio of theaforesaid multiple. the invention the errors transmitted from the leadscrew to the dressing tool are of necessity reduced by the aforesaidmultiple.

The invention will be explained hereinafter with reference of anembodiment illustrated by way of example. The dressing mechanism inquestion can either be built Fig. 1 is a plan view of a dressingmechanism in sec-.

tion'on the line II of Fig. 2, with diagrammatic partillustration of thehydraulic control;

Fig. 2 is a cross-section of the dressing mechanism on the line IIII ofFig. 1;

Fig. 3 is a detail of the dressing mechanism in section on the lineIII-III of Fig. 1;

Fig. 4 is a part-view from the left in the direction of the arrow IV ofFig. 1;

Fig. 5 is a cross-section of the dressing mechanism on the line VV ofFig. 1;

Conse- 7 By this measure according to- 3 Fig. 6 is a cross-section ofthe dressing carriage on the line VIVI of Fig. 1;

Fig. 7 is a side-elevation within the part portion marked VIIVII of Fig.1;

Fig. 8 is a detail of the control-mechanism in section on the lineVIIIVIII of Fig. 6.

Construction of the mechanism for the production of grinding worms Thecasing 1 which is closed laterally by a lid 3 carries a motor 9 attachedto it by means of a flange. The motor shaft 20 thereof is coupled bymeans of a sleeve 10 to a shaft 4 which is in turn rotatably journalledin ball bearings in the casing 1 and lid 3. The shaft 4 carries twogears 11, 12 which are keyed to it. The gear 11 is in mesh with an idlergear 15 which meshes also with a gear 13. The idler gear 15 is rotatablyjournalled in the lid 3 and in a bearing arm 1005 of the casing 1. Thegear 12 is in mesh with a gear 14. The two gears 13, 14 are eachrotatably journalled in two ball bearings 19, 24, respectively, on ashaft 5. Their longitudinal position on the shaft is determined by thetwo end faces 1301, 1401, the aforesaid ball bearings 19, 24, theintermediate rings 27, 28 and circular spring clips 25, 30. The shaft 5is likewise journalled rotatably on ball bearings in the casing 1 and inthe lid 3. It carries in addition to the aforesaid gears 13, 14 thelamellae-clutches 16, 17 respectively associated with them, the clutchsleeve 18 slidably mounted there between, and the two gears 40, 50. Theclutch sleeve 18 is provided with a groove 181 into which two sliderblocks 29 (Fig. 2) are fitted. The latter are pivotally mounted on twopins 26 fixed in the double lever 32. The double lever 32 is pivotallymounted on an axle 22 vertically fitted into the casing 1. The forkedarm of this lever is connected to a piston 37 (Fig. 1) by a pin 33 whichis retained in the piston rod 36. This piston is slidably fitted intothe casing 1. The gear 40 is in mesh with a gear 41 keyed to a spindle6. The latter is likewise rotatably journalled in the lid 3 and casing1, the longitudinal positioning being effected by the two end faces 411,601. On the conical end 602 of the said spindle a flange disc 46 ismounted which is arrested by a screw 44. The flanged disc 46 carriedarworm of abrasive materialhereinafter referred to as the grinding worm45-which is clamped on irnmovably by the aid of a counter flange 47 andof screw 48. The grinding worm is of a single start right hand threadand has in the section perpendicular to the helix angle a toothed rackprofile corresponding to that of the basic rack. A helical thread of thepitch s is to be generated on the grinding worm 45.

The gear 50 keyed on the left hand side end of the shaft 5 forms withthe gears 62, 63, 64 four-partite change gear set which is to beselected and inserted in accordance with the pitch to 'be generated onthe grinding worm 45 (see Fig. 4). The slotted bracket 53 of this changegear set is pivotally mounted on a bushing 49 fixed to the lid 3, andcan be fixed in the position desired by means of a screw 54. The twogears 62, 63 are keyed to a bush 60 which is in turn rotatablyjournalled on a distance sleeve 59 mounted on the pin 57.

The last one, 64, of the said four change gears is keyed to the lefthand side end of the lead screw 7, which is rotatably mounted, parallelto the shaft 6, in the casing 1 and lid 3. It is positioned in thelongitudinal direction by the end face 701 and the nut 69. The leadscrew nut 70 mounted on the threaded portion 702 has a rib 705 (Fig. 2)which is fitted accurately into the longitudinal groove 1001 runningparallel to the axis of the lead screw in the casing 1. By this measurethe said guide spindle nut 70 is restrained from rotating. On top of thesaid nut there is a transverse groove 706 into which a slider block 81is fitted slidably. The latter is on the other hand pivotally centeredon the cylindrical end 771 of a pin 77 which is screwed into the lever75. This lever 75 is keyed to an axle 74, which is rotatably mounted inthe casing 1 .4. about a vertical axis, and is provided with a secondpin 76. The protruding end 761 of the latter pivotally carries a sliderblock 82 which is fitted slidably into a transverse groove 711 of across piece 71. The latter is attached to a shaft 8 by means of aconical pin 72.

A rib 712 arranged on the cross piece 71 engages into a groove 1002,which runs accurately parallel to the axis of the shaft 8. The shaft 8is guided longitudinally slidably in the lid 3 and in the casing 1. Theright hand side end (Figs. 1 and 5) of the shaft 8 which protrudesbeyond the casing 1 is screwed to a spindle 84. Thelatter is rotatablyjournalled in a carriage 85, and a gear 86 is keyed to it, which in turnmeshes with a gear 87. The latter, as well as a hand wheel 39 are keyedon a shaft 88 which is likewise journalled in the carriage 85. Byturning the hand wheel 39 the position of the carriage can be adjustedwhich serves in the first place for adjusting the dressing tool to anexisting thread of the worm. The carriage 85 is slidably fitted on thetwo guide ways 1003, 1004 (Fig. 6). It carries an upper carriage 90, theguide ways 901, 902 (Fig. 5) of which are arranged at right angles tothose of the carriage 85. On the top face 903 of said carriage 90 thedressing tool 98 is attached. In the present case it has the shape of aturning tool the profile of which corresponds to that of the gap of atoothed rack. The dressing tool 98 is held fast by means of a clamp 94,and .is clamped against the top face 903 by the aid of a screw and nut96.

Obviously quite diiferent means could be used for dressing the grindingworm 45, for example a crusher, or a device provided with two dressingtools, each of which operates on one of the two flanks of the grindingworm.

In the upper carriage 90 there is a bore 904 which runs parallel to theguide ways 901, 902 and houses a piston 99. The latter is restrainedfrom rotating by a screw 102 engaging a groove 993, and is screwed to athreaded spindle 106, which is guided and rotatably journalled in thecarriage 85. A band wheel 107 connected to said spindle serves foradjusting the dressing tool 98 in the radial direction.

In order to demonstrate the manner of operation of this dressingmechanism, a hydraulic control system is shown in the presentembodiment. The same comprises a gear pump 122 (Fig. 1) which feedspressure oil from a sump 123 into a pipe 124. The oil pressure iscontrolled by a relief valve 125, while the overflowing oil can bedrained to the said sump through a pipe 126. The pressure pipe 124 isconnected to a valve (Fig. 7) which is in turn in communication with themain control piston 37 and with the piston 99 through various pipes.

Working process As the starting point for the following explanations theconditions of operation may be chosen as illustrated in the Figs. 1 to8.

The motor 9 drives, through the clutch sleeve 10, the shaft 4 with thetwo gears 11,.12.

Since the chamber 371 is connected by the pipe 128 and the chamber 1192(Fig. 8) to the pressure oil pipe 124, while the chamber 372, which isclosed by the lid 38, is connected by the pipe 127 and the chamber 1191to the drain pipe 129, the piston 37 is movedto the left (Fig. 1). Thishas the consequence that to the double lever 32 a force oranti-clockwise torque is applied, and accordingly the clutch sleeve 18is forced to the right (Fig. 1). In these conditions the clutch 17 isengaged, and accordingly the shaft 5 is driven from the gear 12 by thegear 14 in mesh therewith. The gear 13 connected to the clutch 16 whichis set in rotation by the gear 11 through the idler gear 15, runs idly.From the shaft 5 the rotary motion is transmitted on the one hand by thepair of gears 40, 41 to the spindle 6 and to the grinding worm 45 fixedthereto, and on the other hand through the four change gears 50, 62, 63,64 to the left hand thread lead screw'7. The rotation of the lead screw7 causes a displacement of the nut 70'towards the left (Fig. 1). Ofnecessity this displacement effects through the slider block 81 (Fig. 2)a rotary motion in the anti-clockwise direction of the lever 75' (Fig.1). During this rotational movement the slider block 82 centered by thepin 76 carries the cross piece 71 and the shaft 8 connected without playtherewith likewise along to' the left. Through the threaded spindle 84(Fig. 5) screwed to the shaft 8 this displacement is imparted to-thecarriage 85 and ac cordingly also to the carriage 90 and lthe dressingtool 98 fixed thereon, which partake therein. The upper carriage 90 isin the working position. The chamber 991 (Fig. 6) which is incommunication through the pipe 103 to the pipe 128 which at this momentcarries pressure oil, and accordingly this chamber is under pressure.The carriage 90 is forced so far in the direction towards the grindingworm 45 until the lid 105 screwed to it abuts on the piston 99. Thechamber 992 is in communication with the drain pipe 129 through thepipes 104, 127 and the chamber 1191 (Fig. 8). In these conditions thecarriage 85 and the upper carriage 90 move to the left together with thedressing tool 98 (Fig. l). The latter produces the desired helicalthread on the rotating grinding worm 45.

In the embodiment illustrated by way of example the single startgrinding worm 45 has a pitch s. Consequently the dressing tool 98 andthe components 90, 85, 84, 8, 71 connected thereto have to displacethemselves towards the left (Fig. 5), exactly the amount of the pitch sper one revolution of the grinding worm 45. In order to attain thisdisplacement of the magnitude s on the shaft 8, the lead screw nut 70has to perform a movement S (Fig. l). The magnitude thereof isaccurately determined by the proportion s:r=S:R or the equation If it isfurther assumed that R=x.r, the above equation can be rewritten S=x.s

Owing to this lever transmission the faults existing and effective onthe lead screw (errors in pitch, wobbling errors etc.) are nottransmitted in their full magnitude to the shaft 8, the dressing tool,98 and to the grinding worm 45, respectively, but to an extent reducedby the ratio x. Consequently it is possible in this manner to generateon the grinding worm 45 a helical thread which is very accurate asregards pitch and freedom from wobble, with out the necessity of usingan excessively accurate lead screw 7, the production of which wouldhardly be economically bearable.

The stroke described of the dressing tool 98 to the left (Fig. 1) comesto an end when the stop 112 attached to the carriage 85 abuts on thereversing lever 115 (Figs. 6 and 7) and turns the same as well as theshaft 116, journalled in the casing 1, and the lever 117, in theanti-clockwise sense. Consequently the pre-con-trol piston 119 (Fig. 8)is moved towards the right, until it abuts on the lid 121. As soon asthis, has happened, pressure oil can pass from the pipe 124 through thechamber 1192 into the pipe 127. Consequently the chamber 992 (Fig. 6)which is closed by the lid 105 and is in communication with the pipe 127through the pipe 104 is filled with pressure oil. At the same time thechamber 991 is discharged, which is connected to the drain pipe 130through the pipes 103, 128 and the chamber 1193 (Fig. 8). The carriage90 and the dressing tool 98 fixed thereon are pushed back a distance H(see Fig. 6) away from the grinding worm 45. Moreover. pressure oilflows also into the chamber 372 (Fig. 1), while oil contained in thechamber 371 can flow off through the pipe 128 and the chamber 1193 (Fig.8) into the drain pipe 130. The piston 37 (-Fig. 1) consequently movestowards the right and turns the lever 32 in the clockwise direction.Thereby the working stroke clutch 17 is disengaged, the

the latter .as well as the lead screw 7 change their senseof rotation.This change of sense of rotation has the effect that the lead screw nutis carried at once to the right (Fig. 1) while the lever begins to turnin the clockwise direction. To this rotational movement forcibly adisplacement towards the right of the cross piece 71 and of the shaft 8is co-ordinated, in which also the spindle 84, the carriage and theupper carriage with the dressing tool 98 have to partake. At the end ofthe return stroke the abutment 111 fixed to the carriage 85 (Fig. 7)bears on the reversing lever 115 and turns the same, the shaft 116 andthe lever 117 in the clockwise direction. The valve 119 connected to thelatter is accordingly moved towards the left into the positionillustrated in Fig. 8. As soon as this displacement has been carriedout, there 1s communication through the chamber 1192 between thepressure pipe 124 and the pipe 128. Pressure oil flows from the latterthrough the pipe 103 straight into the chamber 991 (Fig. 6) and movesthe upper carriage 90 with the dressing tool 9 8 into the workingpositron. The oil contained in the chamber 992 is returned to the sump123 (Fig. 1) through the pipes 104, 127 and the chamber 1191 (Fig. 8).The chamber 372 is likewise discharged over the same system of pipes. Onthe other hand pressure fluid penetrates now through pipe 128 into thechamber 371 and moves the piston 37 towards the left, which entails atthe same time a rotary movement of the lever 32 in the counter-clockwisedirection, and a displacement of the clutch sleeve 18 towards the right.Thereby the connection with the return stroke clutch is broken, and theworking stroke clutch 17 is engaged. As soon as the reversal controlmovements described hereinabove are terminated, exactly the sameconditions prevail in the whole mechanism and in the hydraulic controlsys tem as those which had been chosen the starting point of thedescrpition of the working process. The grinding worm 45 turns in thedirection indicated in Fig. 1, and the carriage 85 with the uppercarriage 90 and the dressing tool 98 move at working speed from right toleft.

What I claim as myinvention and desire to secure by Letters Patent, is:

l. A mechanism for generating the helical thread on grinding worms forgear grinding machines operating according to the generating principle,comprising in combination: a base, a spindle journalled in the saidbase, and in operation carrying the grinding worm to be dressed, adriving mechanism comprising reversing clutch means mounted in said baseand in operation coupled to the said spindle, a lead screw mechanismmounted in the said base parallel to the said spindle and comprising athreaded lead screw and a lea-d screw nut in screw engagement with oneanother, transmission means journalled on the said base and rotationallycoupling the said lead screw mechanism to the said spindle, a dressingcarriage mounted on the said base slidably in a direction parallel tothe said spindle, a dressing means proper mounted on the said dressingcarriage, lever means pivoted on the said base and engaging the saidlead screw mechanism with a larger lever arm .and the said dressingcarriage with a smaller lever arm transmitting axial movement from thesaid lead screw mechanism to the said dressing carriage at a reducedratio, adjustment means adapted to adjust in operation the said dressingmeans proper in a direction perpendicular to the said spindle, and anautomatic control system responsive to the position of the said dressingcarriage and operatively connected to the said reversing clutch meansand to the said adjustment means, sequentially operating the same,

the chambers of the said cylinders on opposite sides of the said pistonsbeing. alternately connected by the said valve to the said pump and to"thetsaid sump.

References Cited in the file thisp'atent UNITED STATES PATENTS2,286,045- Wickr'nan June 9, 1942 FOREIGN PATENTS 722,871 Great BritainFeb. 2, 1955 879,639 Germany Sept. 27, 1954

